[f. FONT sb.1 + -FUL.] As much as a font will hold.

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c. 1386.  Chaucer, Man of Law’s T., 258.

        She shal have nede to wasshe awey the rede,
Thogh she a font-ful water with hir lede.

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1866.  Blackmore, Cradock Nowell, iii. The tenants and labourers moistened their semi-regenerate clay with many a fontful of good ale, to ensure the success of the ceremony.

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