Referrer comes from refer + -er (agent suffix). Refer is from Latin referre ('to carry back, refer'), from re- ('back') + ferre ('to carry, bear'). The historical chain includes Latin referre and Latin ferre. The quoted older senses, "to carry back, refer", "back", and "to carry, bear", supply the semantic anchors for referrer. The formation is best read as suffixal, compound, and borrowed: the word referrer carries its older form-history into a compact English lexical shape. In present English it is used as a noun, "a person or thing that refers another". Related English forms include refer, referral, reference, and referee. The result is a noun whose etymology preserves both the older form and the later English specialization.