The spelling of /e/ is <e> or <ea>, and the sound occurs in the letter names M, S and X. The spelling of /ɑ/ is <ar> or <a> in command, father, last and khan.
This is a contrast between a long and a short vowel, fairly well separated in the mouth. In spite of the well-known first chapter in The Education of Hyman Kaplan in which he confuses vast first with west and then with vest, it is not a big problem for learners, though slightly more so for learners of US English than of British RP.
The only pairs with taboo words are fetid/farted and S/arse.
Interesting pairs include:
The mean density value is 2%. The pairs make 90 semantic contrasts, giving a loading of 61%.
ate art beck bark becks barks bed baa'd bed bard beds bards belly barley ben barn bens barns Bess baas better barter bettered bartered bettering bartering betters barters blench blanch blenched blanched blenches blanches blenching blanching blessed blast chemist calmest commend command commended commanded commending commanding commends commands Debbie Darby deck dark decker darker deft daft deftly daftly den darn dens darns dense dance denser dancer eft aft ego argot emery armoury Emma amah etch arch etched arched etches arches etching arching etcher archer etchers archers feather father feathered fathered feathering fathering feathers fathers fem farm fester faster fetid farted head hard header harder heady hardy headier hardier headiest hardiest headship hardship headships hardships heavy Harvey heck hark hecks harks helot harlot helots harlots hem harm hemmed harmed hemming harming hems harms hep harp Hetton hearten impellers impalas Ken Calne kennel carnal ken khan kens khans Kent can't kept carped lead lard leaded larded leading larding leather lather leathers lathers ledger larger left laughed legs Largs Len Larne lend larned lens larns lest last level larval M arm Med marred mellow Marlow mesh marsh meshes marshes Met mart Metz marts M's alms neck nark necked narked necking narking necks narks peck park pecked parked pecking parking pecks parks pecker parka peckers parkas pest passed pester pastor pesters pastors pestle parcel pestled parcelled pestles parcels pestling parcelling pests pasts pet part pets parts petted parted petting parting petty party reft raft Reg raj S arse S's arses shed shard sheds shards skep scarp skeps scarps slender slander speck spark specks sparks speckle sparkle speckled sparkled speckles sparkles sped sparred stead starred stet start Ted tarred Teddy tardy ten tarn tens tarns Terry tarry vest vast wrench ranch wrenches ranches wrenching ranching X arcs yen yarn yens yarns
John Higgins, Shaftesbury, January 2011