English 'it' was originally 'hit' in Old English (the 'h' dropped in unstressed speech), and Freud's 'id' is simply the Latin word for 'it' — both descend from the same PIE demonstrative root *ḱi-, making 'it' and 'id' cognates separated by six thousand years.
Used to refer to a thing previously mentioned or easily identified; used as the subject of an impersonal verb.
From Old English 'hit' (it), from Proto-Germanic *hit (it, this thing), from PIE *ḱe- or *ḱi- (this, here), with the neuter suffix *-d. The initial 'h' was lost in Middle English unstressed positions, giving modern 'it.' The PIE demonstrative *id is strikingly similar to Latin 'id' (it, that thing) — the neuter of 'is' (he, that) — which gave English 'id' (Freud's term for the primitive self, literally 'it' in Latin). The neuter gender of the pronoun is thus ancient, traceable to a time before the emergence of natural gender systems
'It' used to be 'hit' — Old English spelled it with an 'h' that was lost in unstressed speech. More remarkably, Freud's 'id' — the primitive, unconscious part of the psyche — is simply the Latin word for 'it.' Freud's original German term was 'das Es' (the It). His translator rendered it in Latin as 'id.' So 'it' and 'id' are the same word from the same PIE root, one through Germanic