1To move from one place to another; to go; to head toward a destination.
明日、東京に行く予定です。
I'm planning to go to Tokyo tomorrow.
学校へ行くバスはもう出ました。
The bus to school has already left.
週末は実家に行きます。
I'll go to my parents' home this weekend.
2To move along or travel through a route or area; to walk along (a road, path).
古い並木道を行くと気持ちがいい。
It's pleasant to walk along the old tree-lined road.
川に沿って行くと駅に出ます。
If you follow along the river you'll come out at the station.
3To turn out/ to proceed (well, badly, etc.); how a situation develops or goes.
プレゼンは思ったよりもうまく行った。
The presentation went better than I expected.
計画が上手く行くか心配だ。
I'm worried whether the plan will go well.
彼と関係が行かなくなった。
My relationship with him stopped progressing.
4To choose or proceed with a particular way or option (often used as 〜で行く).
今回は予算重視で行くことにした。
This time we decided to go with a budget-focused approach.
色はシンプル路線で行こう。
Let's go with a simple color scheme.
5To pass (of time, seasons); to go by.
気がつけば年月が行っていた。
Before I knew it, years had passed.
夏が行き、秋が来た。
Summer passed and autumn came.
6To flow or move (of liquids, gases, blood, etc.); to stream in a direction.
興奮すると血が頭に行く感じがする。
When I'm excited I feel blood rushing to my head.
風は谷を行くように強まった。
The wind strengthened as it moved through the valley.
7To die; to pass away (often written 逝く; a euphemistic expression).
祖父は昨年静かに逝きました。
My grandfather peacefully passed away last year.
あの戦士は若くして逝った。
That warrior died young.
8To reach a stage, extent, age, etc.; to get to a certain point.
彼はもう引退する年齢に行っている。
He is already at the age to retire.
話がそこまで行くとは思わなかった。
I didn't think the conversation would get that far.
9To reach or arrive (of information, instructions, wind, etc.); to be delivered or get to someone/somewhere.
その知らせはまだ彼のところへ行っていない。
That news hasn't reached him yet.
風が谷の奥まで行った。
The wind reached far into the valley.
10Auxiliary used after the -te form to indicate continuation, progression, or a change continuing into the future (〜te iku). In casual speech the 'い' may be omitted.
これからも勉強を続けていくつもりです。
I intend to continue studying from now on.
この調子で行けば、成功するだろう。
If things continue like this, you'll probably succeed.
面倒だから『やってくれ』と言ってしまった（やっていっての短縮）。
Because it was troublesome I ended up saying 'do it for me' (shortened from 'do it and continue').
11Slang for reaching orgasm; to 'come' (colloquial). Often written in katakana as イク.
彼はもうイッてしまったと言った。
He said he already came.
12Slang meaning to trip or get high (drug-induced hallucination or intoxication).
その音楽でみんなイッてしまったと言っている（スラング）。
They say everyone tripped out from that music (slang).