This is a short post about how to avoid literally translating English in a very common set of constructions.
In English, the word ‘one’ pops up all over our syntax like a bad smell. As well as being a number, the source of the indefinite article (even if ‘a’ and ‘an’ no longer look much like it) and an incredibly pretentious personal pronoun, we use it a lot with adjectives and other similar words to express an example of something, an object or a person characterised by the quality of the adjective. Explaining the semantics of words using other words is tough, but you know exactly what I mean: ‘the big one’, ‘the small one’, ‘that one’, ‘this one’.
For indefinites, there is a very similar construction in Arabic:
بدي واحد كبير
biddi waa7ed ikbiir (SYR)
I want a big one [masc]
جبت واحدة جديدة
jibet waa7de jdiide (PAL)
I got a new one [fem]
بدي واحد طويل
baddi waa7ad Tawiil (LEB)
I want someone tall [or a long one, etc]
For definites, though, we absolutely cannot use ‘one’. Instead, a definite adjective is used on its own (or a demonstrative pronoun, etc). (There’s also the construction with ابو or ام, discussed here). Using waa7ed in the following sentences is straightforwardly ungrammatical:
بدي الكبير
biddi likbiir (SYR)
I want the big one
جبت الجداد
jibet lijdaad (PAL)
I brought the new ones
عطيني هداك
3aTiini hadaak (SYR)
Give me that one [masc]
مش هديك, التانية
mish hadiik, ittaanye (JOR)
Not that one, the other one [fem]
This works for relative clauses too:
يلي كان يشتغل عندك
yalli kaan yishtighel 3andek (SYR)
The one who used to work for you
The only place where الواحد works is as a pronoun conveniently similar in meaning (but not in pretentiousness – it’s far more common than its English equivalent) to English ‘one’. Note that it by default takes masculine agreement:
الواحد صار يندم اذا اعترف بحبه
ilwaa7ad Saar yindam 2iza 3taraf b7ubbo (PAL)
These days if you admit you‘re in love you‘ll regret it [= it’s become that one regrets if he admits to his love]