家族全員が集まってパーティーを開いた日は、母の最高の日だった。

family; members of a family

all members (unanimity); all hands; the whole crew; everyone; everybody

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to gather; to collect; to assemble

party

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to open; to undo; to unseal; to unpack; to bloom; to unfold; to spread out; to open (for business, e.g. in the morning); to be wide (gap, etc.); to widen; to hold (meeting, etc.); to give; to open; to found (nation, dynasty, sect, etc.); to open (a new business); to set up; to establish; to start; to open (ports, borders, etc.); to open (an account); to open up (new land, path, etc.); to clear; to develop; to open (a file, etc.); to extract (root); to reduce (equation); to cut open (fish); to change (kanji into hiragana); to flare (e.g. skirt); to slacken (into a poor posture)

day; days; sun; sunshine; sunlight; case (esp. unfortunate); event

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

mother

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

highest; supreme; the most

be; is; indicates past or completed action; indicates light imperative