If this is for Canada, then I think it would be OK to keep the 2×4, but if for Europe, then it might be better to express the size in cm.

At least over here in France, when I want a piece of timber of this sort of size, my wood-yard manager says "Oh, you mean 'chevron'!"

According to my purely empirical observations, wood with a cross-section in these sort of proportions (i.e. relatively 'square', both dimensions of the same order of magnitude, not significantly wider than it is thick) is referred to by different names according to its overall scale — from 'liteau' for the smallest stuff, to 'tasseau' (like GB 2×2 etc.), then 'chevron', and lastly 'madrier' for thumping great beams (as Germaine has pointed out).

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Note added at 1 hr (2012-04-04 16:12:46 GMT)
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Not forgetting 'bastaing'!

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Note added at 1 hr (2012-04-04 16:15:47 GMT)
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In fact, according to this one timber supplier, timber of this sort of scale is called 'bastaing':

http://www.castorama.fr/store/Bois-de-charpente-cat_id_192.h...

(Note: you need to scroll through the 5 pages to see various sizes, and don't take any notice of the generic photos!)

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Note added at 1 hr (2012-04-04 16:17:33 GMT)
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Here's an interesting definition of 'bast(a)ing' from GDT:

"Définition :
Sciage aligné parallèle dont le rapport des dimensions des côtés est compris entre 2 et 3; ces dimensions allant de 55 x 155 à 65 x 185 mm."

So just fits for 4×2!

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Note added at 1 hr (2012-04-04 16:19:17 GMT)
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For what it's worth, here is a GDT entry for 'madrier':

Pièce de bois sommairement équarrie dont les dimensions transversales dépassent un certain minimum (qui varie d'un pays à l'autre).

Sciage aligné parallèle dont le rapport des dimensions des côtés de la section transversale est compris entre 2 et 3, ces dimensions allant de 75x205 mm à 105x225 (AFNOR).

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Note added at 15 hrs (2012-04-05 06:04:14 GMT)
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Definition of 'chevron' found on GDT:

Sciage aligné parallèle de longueur quelconque (généralement plus de 2,50 mètres de long) et de section sensiblement carrée de 40 à 120 millimètres de côté.

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Note added at 13 days (2012-04-18 06:35:50 GMT) Post-grading
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Here's a web page that illustrates several sizes of timber, sadly none corresponding exactly to our case here:

http://www.gaiffe.com/produits.htm

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Note added at 13 days (2012-04-18 06:44:08 GMT) Post-grading
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I don't think this 1:2 ratio cross section is common in France; I know at our local scierie, when I wanted some good old "four-by-two" (what we call it in the UK) to build a studwork partition, they looked at me very oddly and were going to have to cut it specially for me; when I explained what I needed it for, they said "Oh, you want some six-huit' — a squarer section, closer to 'chevron'

Note that 'solive' is also used (= 'joist'), and seems to be more loosely defined — e.g. the web page I cited above classes all the other various forms of wood under the heading 'solive'; however, in UK usage, a 'joist' would usually have a deeper cross section, for example 1:4, as in an 8" × 2" joist, thus bringing it closer to a 'bastaing' (as per the GDT definition mentioned above)