streak vs losing streak

streak and losing streak both are nouns.

Word	Noun	Adjective	Verb	Adverb
streak	Yes	No	Yes	No
losing streak	Yes	No	No	No

As nouns, losing streak is a hyponym of streak; that is, losing streak is a word with a more specific, narrower meaning than streak:

Other hyponyms of streak include winning streak.

streak (noun)	losing streak (noun)
a narrow marking of a different color or texture from the background	a streak of losses
a distinctive characteristic
a sudden flash (as of lightning)
an unbroken series of events

streak (verb)	losing streak (verb)
mark with spots or blotches of different color or shades of color as if stained
move quickly in a straight line
run naked in a public place