My first suspicion was that the Hindi word for friend (दोस्त, dost) would be a masculine noun, then the adjective would change to plural, and the noun remaining the same, I think so. But something in my mind was telling me: why not a feminine Hindi word for "friend" also? Of course, in my native language (Spanish), there are two words, feminine amiga, and masculine amigo, and the plural nouns are amigas and amigos.
Then, I started my travel through the Wiki-sites, as Wiktionary, Wikiversity (Hindi course), other grammar sites, and for a moment I was reading a little about Gujarati and Avestan during my meal. After that, I decided to make a simple question (thinking of the definition in Wiktionary): is दोस्त a Hindi masculine noun? And I could find this (at the same time I decide to put this explanation here, I am afraid of being missing something from the Tips of the course, but I hope this can be profitable also):
-aa (ा) as in l*a*va - general mark of masculine words (singular!) - nouns, adjectives, verbs
-ī (ी) - (ee) - general mark of feminine words (even both - singular and plural) - nouns, adjectives, verbs
Many masculine Hindi words (ending in -aa of course:) can be turned into feminine ones by simply replacing the -aa ending with -ī! For example:
लड़का (laRkaa) = boy, लड़की (laRkī) = girl
बिल्ला (billaa) = tomcat, बिल्ली (billī) = cat, pussycat
Some masculine words ending in -a:
कमरा (kamraa) = room केला (kelaa) = banana तारा (taaraa) = star हवा (havaa) = wind
Feminine Words ending in -ī (-ee):
चीनी (chīnī) = sugar
But exceptions exist. for e.g., the following end in -ī (-ee) but are masculine:
पानी (paanī) = water पक्षी (pakshī) = bird
Some words ending with consonants:
दोस्त (dost) = friend (masculine) किताब (kitaab) = book (feminine) औरत (aurat) = woman (feminine :-)
A word ending in a vowel different from -a or -i:
गुरु (guruu) = teacher
To the general rule of the -a and -i ending there exist some exceptions, that is, there exist some masculine words, which end in -i. For example, the word for "man":
आदमी (aadmī) = man
The same text explains that the general mark for the singular masculine ending -aa is turned to -e to become plural, while the feminine remains the same.
-aa (ा) - general mark of masculine words (singular) - MASC. SG.
-e (े) - general mark of masculine words (plural) - MASC. PL.
-ī (ी) - general mark of feminine words (singular and plural) - FEM. SG. and PL.
-īn and -i~ - occasional mark of feminine words (plural) - FEM. PL.
I really hope it can help. This is intended to bring and share some information. I am still trying to understand better the language, and to learn Hindi words. At least, your simple question has helped me a lot! ;)
Wow, that's a very detailed answer, thank you very much!! I think you are right - dost is (or at least was traditionally) a masculine noun, and so the correct adjective form in the plural would be अच्छे. I was just wondering about this particular sentence, since the subject is feminine plural (Neha and Julia) - I wasn't sure if the word dost would require adjectives inflected for the feminine plural in that case. I did a little bit of research and found this, which suggests that for at least some speakers dost can have both masculine and feminine gender: https://forum.wordreference.com/threads/hindi-urdu-dost-and-gender.2360600/