The Greek noun amoibe means "return," "exchange," or "repayment." It appears once in the New Testament (1 Timothy 5:4) where children are urged to "return" care to their parents.
Paul instructs that children and grandchildren who have a widowed parent should make some return to them — for this pleases God. This encapsulates the theology of gratitude-driven love: we love because He first loved us (1 John 4:19), and we honor parents because God first honored us with life through them.