By the 14th and 15th centuries, the variety of English (Inglis) that resulted from the above influences had replaced Gaelic (Scottis) in much of the lowlands and Norman French had ceased to be used as the language of the elite.

The core vocabulary is of Anglo-Saxon origin although many of the differences in the phonology, morphology and lexicon in the northern and southern dialects of Middle English have been traced to the linguistic influence in the North of the eighth- and ninth-century Viking invaders who first plundered, then conquered and settled in, large territories in Northumbria, Lincolnshire and East Anglia.

During this period a number of words of Anglo-Saxon origin, such as anerly (alone), berynes (grave), clenge (cleanse), halfindall (a half part), scathful (harmful), sturting (contention), thyrllage (bondage), and umbeset (surround), were now almost or completely unique to Scots.

French-derived warfare terms such as arsoun (saddle-bow), bassynet (helmet), eschell (battalion), hawbrek (coat of mail), qwyrbolle (hardened leather), troppell (troop), vaward (vanguard), and vyre (crossbow bolt) became part of the language along with other French vocabulary such as cummer (godmother), disjone (breakfast), dour (stern, grim), fasch (annoy), grosar (gooseberry), ladron (rascal), moyen (means), plenissing (furniture) and vevaris (provisions).

From Scandinavian (often via Scandinavian influenced Middle English) came at (that/who), byg (build), bak (bat), bla (blae), bra (brae), ferlie (marvel), flyt (remove), fra (from), gar (compel), gowk (cuckoo), harnis (brains), ithand (industrious), low (flame), lug (an appendage, ear), man (must), neve (fist), sark (shirt), spe (prophesy), þa (those), til (to), tinsell (loss), wycht (valiant), and wyll (lost, confused).

The Flemings introduced bonspell (sporting contest), bowcht (sheep pen), cavie (hen coop), crame (a booth), furisine (flint striker), grotkyn (a gross), howff (courtyard), kesart (cheese vat), lunt (match), much (a cap), muchkin (a liquid measure), skaff (scrounge), wapinschaw (muster of militia), wyssill (change of money), and the coins plak, stek and doyt.

A number of Gaelic words such as breive (judge), cane (a tribute), couthal (court of justice), davach (a measure of land), duniwassal (nobleman), kenkynolle (head of the kindred), mare (tax collector), and toschachdor (leader, cf.

The reduced set of verb agreement endings in particular give the language an uncannily modern appearance when compared to the writing of English contemporaries such as Geoffrey Chaucer.