يَرْتَجِل

improvise(verb)

to compose and perform (a poem, tune etc) without preparation

The pianist forgot his music and had to improvise.

يَسْتَنْبِط عَلى الفَوْر

improvise(verb)

to make (something) from materials that happen to be available, often materials that are not normally used for that purpose

They improvised a shelter from branches and blankets.