I am sure you have heard of the word "ไม่ได้" (mâi-dâi) and everybody would tell you that it means "cannot" 

What about "ไม่ไหว" (mâi-wǎi)? 

This one also means "cannot" but in the sense of "cannot anymore" due to whatever reasons. This word is usually accompanied by the word "แล้ว" (láew) which means "already" at the end.  

Beside this, ไม่ไหว" (mâi-wǎi) can also means "physically cannot." And when it means "physically cannot do something", you don't need  "แล้ว" (láew) at the end, unless you want to say "cannot ANYMORE."

Examples for both cases:

1. ฉันอิ่มมาก กินไม่ไหวแล้ว (Chǎn ìm mâk. Gin mâi-wǎi láew)

    I am soooo full! I can't eat anymore.

2. ฉันทำโปรเจคนี้มาทั้งคืนแล้วนะ ทำไม่ไหวแล้ว (Chǎn tam project ní maa táng-keun láew ná. Tam mâi-wǎi láew)

    I've been doing this project the whole night. I can't do it anymore!

3. พวกเราเดินมา 4 ชั่วโมงแล้วนะ ผมเดินไม่ไหวแล้ว (Puâk-rao dern maa sì chuâ-mong láew ná. Pǒm dern mâi-wǎi láew)

    We've been walking for 4 hours already. I can't walk anymore.

4. ทนไม่ไหวแล้ว (Ton mâi-wǎi láew)

    I can't take it anymore!

5. รอไม่ไหวแล้ว(Raw mâi-wǎi láew)

    I can't wait anymore!

6. ฉันยกรถไม่ไหว (Chǎn yók ród mâi-wǎi)

    I can't lift the car.

7. ฉันขยับตู้เย็นคนเดียวไม่ไหว มันหนักเกินไป  (Chǎn kà-yàb dtû-yen kon-deao mâi-wǎi. Man nàk gern-bpai.)

    I can't move the refrigerator alone. It's too heavy.

I hope that the content above was clear to you. If you have any further questions, please feel free to shoot me a message.