The entirety of Exodus 20:13 is one word: 'xcr' or 'ratsach' (Strong's number 07523) used in the qal tense (imperfect).

What does this word mean:

  1. to murder, slay, kill
    1. (Qal) to murder, slay
      1. premeditated
      2. accidental
      3. as avenger
      4. slayer (intentional)
    2. (Niphal) to be slain
    3. (Piel)
      1. to murder, assassinate
      2. murder, assassin
    4. (Pual) to be killed

The use of ratsach continues to be used throughout the Old Testament, most notably in Numbers 35 (verses 6, 11, 12, 16-19, 21, 25-28, 30, 31) which cover the refuge for accidental killers and again as specific acts in Judges and 1 Kings which are murders and assassinations - not wartime killing.

The ideas of one language do not always clearly map into another language, and this is certainly the case with ratsach - it does cover the same set of ideas as 'kill' and 'murder' in English. In some cases it covers more 'thought space' and in other areas less.

One possible word that may more closely fit that of the Hebrew meaning is 'manslaughter' or killing in anger. While this does not appear to cover all instances, it is a starting point.

Looking at other verses (Judges 20:4, 1 Kings 21:19, Job 24:14, Psalms 62:3, Proverbs 22:13, and Hosea 6:9) another image of ratsach begins to emerge - that of a predatory animal. This is especially clear in Proverbs 22:13 ("The slothful man saith, There is a lion without, I shall be slain in the streets." - here ratsach is translated as 'slain').

This differs from the use of the word nakah which has the approximate meaning of 'to strike' (David nakah Goliath). This act is one of judgment.

Returning to the original question - do soldiers break the commandment of 'thou shall not kill'? The answer in almost all cases is that of 'no'. However, there are times when people go out and prey upon others in such a manner as a predator. We call these instances when they are discovered 'atrocities' and 'war crimes'.

Albeit a tangent, it is something that is interesting when the word study of ratsach is fresh in the mind. In 'thou shall not kill', it the word in no way relates to that of capital punishment. There is no anger in the action nor predatory behavior on the part of those carrying out the sentence.