彼はとても疲れていたので、ぐっすりと眠り込んだ。

Since he was very tired, he fell sound asleep.

彼(かれ)はとても疲(つか)れていたので、ぐっすりと眠(ねむ)り込(こ)んだ。

Kare wa totemo tsukareteita node, gussuri to nemurikonda.

彼 (かれ)

he; him; his; boyfriend

は (は)

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

迚も (とても、とっても)

very; awfully; exceedingly; (not) at all; by no means; simply (cannot)

疲れる (つかれる)

to get tired; to tire; to be worn out (e.g. of well used objects); to starve

ので (ので、んで)

that being the case; because of ...; the reason is ....; given that...

ぐっすり (ぐっすり)

sound asleep; fast asleep

と (と)

if; when; and; with; particle used for quoting (with speech, thoughts, etc.); quoting particle; promoted pawn; indicates question (sentence end)

眠り込む (ねむりこむ)

to fall asleep; to sleep deeply

Readings: ヒ、かれ、かの、か.の

Meanings: he, that, the

Readings: ヒ、つか.れる、 -づか.れ、つか.らす

Meanings: exhausted, tire, weary

Readings: ミン、ねむ.る、ねむ.い

Meanings: sleep, die, sleepy

Readings: -こ.む、こ.む、こ.み、 -こ.み、こ.める

Meanings: crowded, mixture, in bulk, included, (kokuji)