colloquial form of “weak”; feeble or puny (physically, mentally, or in effect); lacking strength or robustness.
彼は体が弱っちいので、夜遅くまで働けない。
He has a weak constitution, so he can't work late into the night.
あの説明は弱っちくて、誰も納得しなかった。
That explanation was weak and nobody was convinced.
そのおもちゃは作りが弱っちくて、すぐ壊れてしまった。
That toy was poorly made and broke right away.