What's the difference between overcast and overmast?

Overcast

Definition:

(v. t.) To cast or cover over; hence, to cloud; to darken.
(v. t.) To compute or rate too high.
(v. t.) To take long, loose stitches over (the raw edges of a seam) to prevent raveling.

Example Sentences:

(1) Techniques involving a cemented porcelain-fused-to-metal overcasting have often been successful in restoring the fixed partial denture to form and function.
(2) Murky crime drama Shetland (Tuesday, 9pm, BBC1) returns this week for a second series, revealing Shetland as the most eerie – and overcast – location on Earth.
(3) Smoke continued to swirl into an overcast sky more than an hour after the reported explosion as witnesses in the area gave accounts of feeling a shock wave.
(4) Winter depression, a form of seasonal affective disorder, is a common condition that increases in prevalence in northern areas and in regions with a high proportion of overcast fall and winter days.
(5) I like photographing overcast days and people looking sad.
(6) Ten males participated in the event which took place on a cool, overcast day and consisted of a 1.0-km swim, a 30-km cycle ride, and a 10-km run.
(7) Dentists have frequently used overcastings to avoid removal of the restoration.
(8) The morning is overcast – calm, cool and quiet, almost Zen-like.
(9) It’s a bleak, overcast day when the Guardian visits Rose Hill.
(10) It’s an overcast morning when I start my 155km walk along the Berlin Wall Trail, the Mauerweg, and the granite skies make the scarred, concrete remnants of the Wall along Bernauer Strasse look even more sinister than usual.
(11) But the clan believes that if the sky is overcast, the scars will continue to weep.
(12) Parts of Ohio are high-risk areas given the high percentage of overcast days.
(13) An overcasting was fabricated and was permanently cemented on each preparation.
(14) There was less activity on partly overcast days than on clear days.
(15) Sir Bobby Charlton, his own life in football so overcast by Manchester United's tragedy at Munich, handed the Liverpool legend Ian Rush a bouquet of roses as a symbol of fraternity.
(16) Those hoping for a bank holiday weekend to banish the bad weather should prepare for disappointment: the Met Office has warned that, while the torrential rain of recent days should subside, many areas could still see overcast skies, occasional showers and night-time temperatures falling below freezing.
(17) It claims to offer 99 Oregon beers on tap and, though I can’t personally vouch for all, the Ancestry Golden was light, the Yachats was smooth, the Block 15 was malty and the Oakshire Overcast Espresso Stout was a creamy, energising shot of success.
(18) The technique involves intradermal overcasting with monofilament non-resorbable suture covered with a double adhesive film which reduces strain and provides a therapeutic pressure; after ablation of the first film, it is replaced with adhesive films continuously for 2 months.
(19) Magnets glued to the backs of experienced pigeons often resulted in disorientation when the birds were released from distances of 17-31 miles (27-50 km) under total overcast, whereas no such disorientation occurred during similar releases under clear skies.
(20) On Wednesday, however, for at least one afternoon, all was right at AT&T Park, and that's because Lincecum tossed his second career no-hitter, bringing a bright finish to an overcast day in the Bay Area.