Late Middle English; earliest use found in Promptorium Parvulorum. From south + -ly. Compare West Frisian súdlik, Middle Dutch sudelijc, zudelijc (Dutch zuidelijk), Middle Low German sǖtlīk, German südlich, Danish sydlig.
Definition of southly in US English:
southly
adjectiveˈsaʊθli
Southern; southerly.
Origin
Late Middle English; earliest use found in Promptorium Parvulorum. From south + -ly. Compare West Frisian súdlik, Middle Dutch sudelijc, zudelijc (Dutch zuidelijk), Middle Low German sǖtlīk, German südlich, Danish sydlig.