I was watching The Web Of Fear (one of the lost episodes). In episode 5, the Great Intelligence says that if The Doctor doesn't comply then it will "have to seek the help of lesser mortals - like your companions here!".
Is there an earlier in-universe reference to the term "companion"?
The term "companion" is used more outside the programme — which is to say in fandom — than within the narrative. It was especially rarely used in the original version of the television programme and practically never uttered by the Doctor himself