noun
noble gas
Chemistry term for the group of inert gases such as helium, neon, argon, etc.
ヘリウムは希ガスの一種です。
Helium is a type of noble gas.
expression
I get the feeling that ...; I think that ...
Only when written 希ガス
Internet slang pun on 気がする; used humorously to express a hunch or impression. Restricted to the 希ガス spelling.
See also: 気がする
明日は雨が降る希ガス。
I have a feeling it will rain tomorrow.
Standard expression meaning 'I have a feeling that...'; 希ガス is a playful internet slang version.
From 希 (rare) + ガス (gas), a calque of 'noble gas' or 'rare gas'. The slang sense is a pun on 気がする.