Actually, i think Thanos would wax Android 18. Even DBS showed that people with non-conventional powers are like poison for most of these and Androids can get damaged like anyone else.
Thanos would probably turn 18 into an infinite battery for a weapon or just teleport her directly into a sun. Thanos is way too durable for baby non-High tier super characters to match.
Same reason Silver Surfer is a bad matchup for DBZ people too. The ability to absorb, drain, and redirect energy is a huge advantage.
Thanos could just mind-rape 18, teleport her into a sun/blackhole, and he beats down people who walk through suns/supernovas/black holes like they're nothing.
Android 18 toyed with Super Saiyan Vegeta and broke his arm, knocked out Piccolo with one hit and IIRC knocked Super Saiyan Trunks out with one hit. Not to mention she has superspeed while Thanos is prolly not even faster than Captain America. Thanos is comparable to Namek era Frieza without super speed imo.