The Greek noun akrothinion (from akron = top/tip + this = heap) literally means 'the top of the heap' — the choicest part, the firstfruits of a pile of goods or spoils. It was used in classical Greek of the best part of war spoils dedicated to the gods, and in Hebrews 7:4 it describes what Abraham gave to Melchizedek.
The single New Testament use of akrothinion in Hebrews 7:4 is theologically significant: 'See how great this man was to whom Abraham the patriarch gave a tenth of the spoils!' Abraham, who had just defeated four kings and recovered Lot, gave Melchizedek — the priest-king of Salem — the choicest portion of the plunder. This act establishes the argument of Hebrews 7: that Melchizedek's priesthood is greater than Abraham's (and therefore greater than the Levitical priesthood descended from Abraham). The author is building toward the climactic point that Christ, our High Priest 'in the order of Melchizedek,' holds a priesthood far superior to the old covenant. The akrothinion Abraham gave Melchizedek prefigures the offering every believer brings to Christ — the firstfruits, the very best, laid at the feet of our eternal High Priest.