เสร็จ [sèt] to finish, to be done.

e.g.
ทำงานเสร็จยัง [tam ngaan sèt yang] Have you finished working yet?
ว่ายน้ำเสร็จแล้ว [wâai náam sèt léaw] I’ve finished swimming.
กินเสร็จแล้วบอกนะ [gin sèt léaw bàwk ná] Tell me when you’re done (eating).

จบ [jòp] to be over, to end.

e.g.
หนังจบยัง [nǎng jòp yang] Is the movie over yet?
ฉันเรียนจบคณะวิทยาศาสตร์ [chán rian jòp kaná wíttayaasàat]
I graduated (I completed my studies) from the school of Science.
หนังสือเล่มนี้สนุกมาก อ่านวันเดียวจบเลย [nǎng sěu lêm níi sanùk mâak àan wan diao jòp loei]
This book is really fun to read. I finished reading it in one day.
(I read it from the beginning to the end)

เลิก [lêrk] to end, to quit, to stop.

e.g.
ผมเลิกงานหกโมงเย็น [pǒm lêrk ngaan hòk moong yen] I get off work at 6PM.
เขาไม่ยอมเลิกแกล้งฉัน [káo mâi yawm lêrk glâeng chán] He won’t stop making fun of me.
แฟนผมเลิกสูบบุหรี่เพื่อผม [fan pǒm lêrk sùup burìi pêua pǒm] My girlfriend quit smoking for me.

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