In the 1978 Battlestar Galactica series the main Cylon ship was always called a baseship. In what episode was it ever called a basestar in 1978? The basestar name was used in the 2004 series only that I can recall.
I don't have the originals to hand, but the transcripts here suggest that base star was used in multiple episodes. Early examples:
Saga of a Star World:
IMPERIOUS LEADER I will send with you a base star, entirely under your command. Lucifer?
Lost Planet of the Gods:
BALTAR As they did at Carillon? Hmm? Hm. One base star is not sufficient to assure victory over the Galactica. Find her, but follow just beyond her scanner range.
The Gun on Ice Planet Zero:
RIGEL Cylon base stars, quadrant Epsilon, closing rapidly.
The Living Legend:
ADAMA Good Lord! A Cylon base star?