The following is a list of arabic words used normally in conversations:
Akhi - Brother
Ukhti - Sister
JazakAllah - May Allah give you Ajar/Sawab for your deed.
MashAllah - As God has willed.
HayakAllah - May Allah give you life.
BarakAllahu Feek - May Allah put barkah in what you are doing.
wa feeka barakallahu - and May Allah bless you. (in response to Barakallahu Feek)
Wa iyyakum - And to you
Alhamdu lillah - Praise be to Allah
Allah - God
Allahu Akbar - Allah is Most Great
Amanah - Trust
Assalamu Alaikum - Peace be upon you--the "official" Islamic greeting.
Assalamu Alaikum wa Rahmatullahi wa Barakatuh - "Peace and the Mercy and Blessings of God be upon you" Extended form of the above.
Astaghfir Allah - I seek forgiveness from Allah (used when mentioning something that goes against the standards of Islam)
Ayah/Ayat - Qur'anic verse
Bid`ah - Innovation, addition to the religion's essentials
Bukhari - One of the most noted compilers of hadith. His collection is known as Sahih Bukhari
Bismillah ar-Rahman ar-Rahim - In the Name of Allah, the Most Gracious, Most Merciful
Da'wa - Invitation (for humankind to Islam)
Du`aa - Supplication
Eid - Islamic holiday
Fatwa - Islamic legal ruling
Fiqh - Islamic law as interpreted by scholars
Fitnah - Corruption and disorder, also temptation
Hadith - A report of a saying or deed of the Prophet
Haj - Pilgrimage
Halal - Allowed (per Islamic law)
Haram - Forbidden (per Islamic law)
Hazrat/Hadrat - Honorable
Hijab - Modest way of behavior and dress (including head scarf for women)
Imam - Leader
Iman - Faith
In Shaa Allah - If God wills. (Used when talking about a future event)
Injeel - The scripture sent down to Prophet Issa (Jesus)
Isnad - Chain of transmitters, the list of people who successively narrated a given hadith
Jannah - Paradise
Jazakallah Khair - May God grant you what is good. (Often used instead of "Thank you")
Jihad - Striving for Islam, whether by peaceful or violent means (NOT holy war!)
Jinn - Unseen beings, who, like humans, are given the power to choose between right and wrong
Kafir - One who denies the truth. Literally, one who "covers" the truth (sometimes applied to non-Muslims).
Khalifah - Caliph: Leader of Muslim nation
Khilafah - Caliphate
Khutba - Sermon
Kufr - Denial of the Truth, rebellion against God
La Ilaha Illa Allah - There is no deity but God
Ma Shaa Allah - What God has willed! (Usually used to express wonder at Allah's creation)
Madhhab - School of jurisprudential thought
Makruh - Detested, but not forbidden (per Islamic law)
Mandoub - Recommended, but not required (per Islamic law)
Mubah - Neither forbidden nor commended. Neutral (per Islamic law)
Mushrik - One who commits Shirk
Muslim - One who submits to Allah and is a follower of Islam; also, name of one of the most notable hadith scholars. His collection is known as Sahih Muslim
Nabi - Prophet
Qur'an - The Words of Allah conveyed to us by the Prophet
PBUH - Peace Be Upon Him. Same as SAW
RAA - (Radia Allahu Anhu/Anha.) May Allah be please with him/her
Rasool - Messenger (Prophet to whom a scripture is revealed)
Rasool Allah - Messenger of God (used to refer to Prophet Muhammad)
Sahaba - Companions of Prophet. Singular is "Sahabi"
Sahih - "Sound in isnad." A technical attribute applied to the "isnad" of a hadith
Salaam - Peace. An abbreviated version of the Islamic greeting
Salaat - Prayer
SAW - (Salla Allahu Alaihi Wa Sallam.) Peace Be Upon Him
Sawm/Siyam - Fasting
Seerah/Sirah - History of the Prophet's life
Shahadah - Bearing witness that there is no god but Allah and that Muhammad is His Messenger.
Shari'ah - Divine Law
Sheikh - Scholar (or any elder and/or respected man)
Shirk - Associating partners (e.g. helpers, other gods) with Allah
Shura - Consultation among Muslims
Subhan Allah - "Glory be to God"
Sunna/Sunnah - Tradition of the Prophet
Surah/Sura - A Chapter in the Qur'an
SWT - (SubHanahu Wa Ta`ala.) Glory be to Him. Used only in reference to Allah
Tafsir - Interpretation
Tawraat - The scripture sent down to Prophet Musa (Moses).
Ulama - Religious scholars
Umma - Nation, community.
Ustadh - Teacher
Wassalaam - And peace. It means "goodbye"
Zakat - Required charity