Old English trum 'strong,' truma 'host': Welsh trwm 'heavy.'

OLD English trum |strong, firm' is simplex for an important group of words, including the compounds for |host, troop', folctrum, scildrum; getrum, folcgetrum, fyrdgetrum; truma, gartruma, scildtruma; and getruma and angetruma, as well as wyrttruma |root' and trymman |strengthen'.

Of these, two words surviving in Middle English are trume |troop', found in Layamon, Hali Meiohad, and Havelok; and sheltron |phalanx', in Layamon, Sir Orfeo, Robert Mannyng's Chronicle, Barbour, Morte Arthure, the Wycliffite Bible, Trevisa, and Langland. Modern English trim may also go back to OE trymman, and shelter to OE scildtruma, ME sheltron, Unfortunately, OED notes that, while formally the verb trim could come from the Old English verb, we lack unequivocal connecting evidence from Middle English; and that derivation of shelter (unattested before 1585) from sheltron also creates difficulties, partly dispelled by the line |Heyle scheltrim schouris to shelde' in a late medieval Marian lyric.(1)

Yet trum as evidently a productive form in Old English. It is surprising that an etymology seems unknown. OED, s.v. trim, notes that OE trum |firm, stable, strong, sound, robust' has no cognate in other Germanic languages, but draws attention (as |possibly bearing' on the history of the word) to the compounds getrymman |to confirm, strengthen, encourage', and betrymian |to beset with a force, besiege, environ', with three examples of the latter as late as c. 1225.

No attempt seems to have been made to derive Old English trum from Brittonic trum (Modern Welsh trwm), defined as |heavy, sad, wretched; battle, adversity', and to regard it as a military loanword borrowed by the English from their Celtic enemies in the sixth century. Nevertheless, this appears to be consistent with the evidence.

Welsh trwm is well attested. …