I know it sounds strange, but I think it's probably the term used. I've come across eyebrow in other technical contexts, and it seems that it is also used in architecture.

The link below is just an example of an 'eyebrow window' ...

HTH

Mary

I think this typically Romansque feature could be called a semi-circular arch in English.

HTH

Sheila

The defining feature of the Romanesque Revival is the semi-circular arch used for all window and door openings and for wall enrichment. Other distinguishing motifs are beltcourses and the arcaded corbel table which is a series of miniature arches below the eaves. Belt- or stringcourses mark horizontal divisions. Column capitals and compound arches are enriched with geometric medieval ornament. Facades have gabled roofs flanked by square or polygonal towers of differing heights, with parapets or various roof shapes, and occasionally spires of Gothic origin. Pyramidal roofs often have concave slopes. The typical plan is basilican, with a long, narrow nave, vestibule, central tower or paired side towers, and self-containedmassing. Broad, smooth wall surfaces of monochromatic brick or ashlar masonry laid with thin mortar joints were favored.



http://www.sacredplaces.org/PSP-InfoClearingHouse/articles/T...

'Sourcil chenfreiné' is 'hollow chamfer'. A chamfer is the surface made when the sharp edge (arris) of a stone block or piece of wood is cut away, usually at an angle of 45° to the other two surfaces. It is called a 'hollow chamfer' when the surface made is concave (like an eyebrow!).
Reference - my own History of Art studies at university and the definition from the Penguin Dictionary of Architecture.

It seems to me this could be the kind of raised stone moulding that is often encountered above arches, sticking out to prevent water running down the wall above from reaching the window.

This protudes in exactly the same way as an 'eyebrow', and is usually 'chamfered'

I've heard the term 'dripstone moulding', but am not certain if this is exactly the same thing.

Perhaps that may help you along thre right track, and someone else will be able to give you the precise technical term?

Good luck!

The reference below includes, in a litany of complaints about improper terminology, the following:
"un sourcil servant à désigner le cordon saillant qui contourne une archivolte"

This is quite consistent with Dusty's remark, taking into account the current context. We want the term for an externally projecting chamfered molding surmounting a window and extending beyond it.

Too hard for me, but I hope this is of some help.

incidentally dripstone sort of sounds like larmier to me, but this is all too subtle for me.