Peace,
'Junub' in the context of verse 4:43 refers to a state that is caused by sexual intercourse and discharge of semen.
"He was, or became, in the state of one who is termed جُنُب; (S, IAth, Mgh, L, Msb, K;) i. e., under the obligation of performing a total ablution, by reason of sexual intercourse and discharge of the semen." [1]
I hope this helps, God willing
Regards,
Joseph
REFERENCE:
[1] LANE. E.W, Edward Lanes Lexicon, Williams and Norgate 1863; Librairie du Liban Beirut-Lebanon 1968, Volume 2, Page 465