"Step" would fit there...
"Skep" would also fit (def. a straw beehive)
Skew
Stew
spew
slew
seed
sped
sled
seer
sees
seem
seep
seek
seen
shed
shew
sked
form, fort, fore, norm, worm, worn
Nothing in English.
Slits
seesaw
Sites
gusset
sepsis
The word could be execs.
ladybirds, calyptras, kalyptras, capybaras
pens lens legs
Some choices for _as_er are:bastercasterdashereasierEasterfasterjaspermashermasterrashertastervasterwasherwaster
There are over 100 words that can fit this:AramesBracesBrachsBractsBraidsBrailsBrainsBrakesBrandsBranksBrantsBravasBravesBravosBrawlsBrawnsBrazasBrazesCraalsCracksCraftsCrakesCrampsCranesCranksCrapesCrasesCrasisCratesCravesCrawlsCrazesDraffsDraftsDrailsDrainsDrakesDramasDrapesDrawlsErasesFracasFrailsFramesFrancsFranksFraudsGraalsGracesGradesGradusGraftsGrailsGrainsGramasGrampsGrandsGrantsGrapesGraphsGraspsGratesGratisGravesGrazesIradesKraalsKraftsKraitsKrautsOrangsOratesPraamsPrahusPrangsPranksPrasesPratesPrawnsPraxesPraxisTracesTracksTractsTradesTragusTraiksTrailsTrainsTraitsTrampsTranksTranqsTrapesTravesTrawlsUraeusUraresUrarisUrasesUratesWracksWrangsWraths
bust base busk busy bush
Fish
dispossess