So as the title indicates, I'm wondering about exactly what is the difference between all the existing words that mean "smile", I originally learned only 笑い, which I feel is the most regularly used one (although it can also means a laugh), but as I'm learning I started coming across at least ten other word that are all translated in english as smile, and so I wondered where exactly was the difference. These are the following words I've encountered (besides warai) :
They are, in Japanese term, all subcategories of 笑い, the widest word that covers both loud laugh (giggle, chuckle etc.) and silent smile (grin, smirk, simper etc.)
笑み/笑顔
The two words are related to every kind of silent happy face (abovementioned). 笑み is the action itself (< verb 笑む), but is a bookish word that hardly appears in conversation. 笑顔 is more popularly used one that refers to the face (or expression), and we usually call making smile 笑顔を作る.
微笑【ほほえ】み/微笑【びしょう】
Literally "dim happy face", may be the most exact words correspond to English smile. However, these are a bit more nuanced than the English counterpart where they're associated with affection, dearness or benevolence, that don't fit every situation we could use smile. The most typical usage would be 天使の微笑み "angel's smile".
微笑【びしょう】 is the Sino-Japanese synonym of 微笑【ほほえ】み, thus sounds loftier. Note that the last okurigana of 微笑み isn't obligatory, so sometimes you'll see 微笑 is read ほほえみ too.
一笑
This is somewhat an odd one out, and has most limited range of usage. It has two meanings: making a friendly happy face lightly/briefly as in 破顔一笑 "(break into) a broad smile"; and laugh something down/off as in 一笑に付す. Both are often seen in literary works.
にっこり
This is a mimetic word depicts such a sunny smile:
for this kind of evil smile, we use にやにや or にやける (verb), which is frequently heard in anime when girls rebuke guys that have dirty mind.
and for big grin, we prefer にんまり.
BONUS
We also use English loanword スマイル, usually for the cheerful smile or grin which Americans are particularly good at.
(for illustrative purposes only)
Yeah this is funny concept in Japanese because the most common word used to refer to the smile is 笑顔 which doesn't refer to the just the smile itself but rather the smiling face taken as a whole. The actual smile itself I believe is referred to as 微笑み though it's not nearly as common. にっこり is more of an adjective used to describe someones behavior - like for example you walk into a room and someone you know has this oddly suspicious smile on their face and you ask them "what the hell are you so smiley about?". 笑い is more like the act of laughing than just smiling.
The main concept though is that whole smiling face is usually the thing that is referred to.
