Gulf Arabic Grammar
...G.2.1. Definite Article ...G.2.2 Personal Pronouns ...G.2.3 Possessive Pronouns ...G.2.4. Possessives with maal- ...G.2.5 Commands and Requests ...G.2.6 Broken Plural ...G.2.7 Plural -aat ...G.2.8 Plural -iin ...G.2.9 Plural -iyya ...G.3.1 The Construct State - iDaafat ...G.3.2 The Dual Form ...G.3.3 Adjectives ...G.3.4 Personal Pronoun Suffixes ...G.3.5 Prepositions ...G.3.6 To Have, 3ind- ...G.3.7 Past Tense I ...G.4.1 More on Adjectives ...G.4.2 Comparison Forms ...G.4.3 Numbers: Cardinals and Ordinals ...G.4.4 Telling the Time ...G.4.5 Question Words ...G.4.6 This, That, These (Demonstrative Pronouns) ...G.4.7 Past Tense II

Gulf Arabic Grammar - The Broken Plural

We could say Arabic is quite a lot about roots and patterns. As the famous example goes the three consonants k-t-b convey the meaning of ‘writing’. Hence kitab - he wrote, kaatib – writer, maktuub – written, a letter, maktab – office (a place where a lot of writing happens), maktaba – library, etc.

If we let the letter C represent a consonant (in this case k or t or b), we could represent the above words with the following patterns:

kitab CiCaC (verb, Past Tense)
kaatib CaaCiC (Agent Noun)
maktuub maCCuuC (Past Participle)
maktab maCCaC (Noun of Place)
maktaba maCCaCa (Noun of Place)

That said, many frequently-used nouns (and some adjectives) form their plural by breaking up their internal shape. You can see these in English in just a few words, e.g. ‘goose‘ becomes ‘geese’, ‘mouse’ becomes ‘mice’, ‘woman’ becomes ‘women’ etc.

In this section (V.2.x/G.2x) of the Gulf Arabic course you encountered several examples of ‘broken plurals’, some of which are:

suug -> aswaag (market/s)
rayyaal -> rayyaayyiil(man/men)
sadeeg -> asdigaa (friend/s)
3aamil -> 3ummaal (worker/s)

Usually, short nouns take a broken plural. This includes many words borrowed from other languages as long as they are short in length: film -> aflaam (film/s), kart -> kuruut (card/s), bank -> bunuuk (bank/s).

Below are some common ‘broken plural’ patterns. The first two patterns denote proffesions and occupations.

1). Singular CaCCaaC or CiCCiiC -> plural CaCaaCiiC

2.) Singular CaaCiC‘: plural CuCCaaC

Examples:
najjaar (carpenter) -> najaajiir
3aamil (worker) -> 3ummaal
7aakim (ruler) -> 7ukkaam
kaatib (clerk, writer) -> kuttaab
taajir (trader, merchant) -> tujjaar

3.) A variation of 1.) is CiCCiiC -> plural CaCaaCiiC

sikkiin (knife) -> sakaakiin

4.) plural CuCuuc

bayt (house) -> buyuut
galb (heart) -> guluub
gasir (palace) -> gusuur
shayx (sheikh) -> shuyuux

5.) plural aCCaaC

xabar (a piece of news) -> axbaar (news)
film -> aflaam
suug (market, marketplace) -> aswaag
ragm (number) -> argaam

6.) plural CiiCaaC

jaar (neighbour) -> jiiraan
baab (door) -> biibaan

7.) plural CaCaaCic

maktab (office) – makaatib
maTbax (kitchen) – maTaabix
mat7af (museum) – mataa7if
masjid/masyid (mosque) – masaajid/masaayid

You will have to learn the plurals together with the singulars. You will gradually develop sort of an intuition as to what the plural of a particular word might be.