paying back in installments; amortization
Original meaning: repayment of a debt in small, gradual installments. Now somewhat dated; the extended sense (sense 2) is far more common.
We agreed to pay back the debt in installments.
gradual progression; doing little by little; drifting into a state
Most common modern use. Describes a process that advances step by step, often without a clear plan, and frequently leading to an undesirable or unintended situation. Often used adverbially as なし崩し的に or なし崩しに. Sense 3 (colloquial) adds a nuance of vagueness or quiet fading, but the core idea is the same gradual, unstructured progression.
The plan was gradually postponed, bit by bit.
I ended up taking on the work little by little without really deciding to.