Lit. 'a military expedition', hence host. Before the Norman Conquest, the *AS militia or military host. Fyrd-service formed a part of the *trimoda necessitas owed to the king. Failure to present oneself was subject to heavy fines: a *thegn was liable to forfeiture, while a retainer would owe his lord 40s for not attending. In Henry I's reign the fine was 120s. -
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.